Uninterruptible power supplies are required for many computer installations such as network file servers, telecommunications equipment or other applications where a sudden loss of power would create an unacceptable and costly occurrence. For example, there may be situations where data would be lost or corrupted if power were lost during a data transfer or perhaps the cost of a business shutdown simply because of the unavailability of a computer would be sufficient to justify the additional cost for an uninterruptible power supply. Thus, for various reasons there are numerous applications where an uninterruptible power supply is required and the numbers of these applications would each increase substantially if the cost were reduced.
Presently available uninterruptible power supplies are placed between the standard AC utility outlet and the AC utility plug for the computer or other electrical device which must receive continuous electrical power. The power supply includes a battery providing electrical energy in the event of a power failure, an AC to DC converter and an inverter converting electrical energy back from DC to AC. The standard device power supply then receives the AC input from the uninterruptible power supply and in turn converts this to the various required regulated and unregulated voltages required for the system. The AC to DC converter of the conventional uninterruptible power supply converts the AC power to DC power at approximately the battery voltage with a trickle charge being available to assure that the battery remains charged at all times. Typically the battery is a lead acid battery. The inverter then reconverts the DC energy from the DC battery voltage back to an AC power supply approximating standard utility AC power. In the event of a power failure, the internal DC voltage from the AC to DC converter drops below the battery output voltage. This causes the battery to begin supplying the DC power to the inverter in lieu of the AC to DC converter. The system proceeds with the battery supplying power until standard AC utility power is restored or the battery discharges.
While such arrangements work satisfactorily, they are relatively expensive and inefficient. Such systems must work at relatively high power levels of typically two hundred to three hundred watts and are typically only 75 to 80 percent efficient. Consequently, substantial amounts of power must be dissipated within the uninterruptible power supply. Large and expensive components are therefore required to dissipate the resulting heat. In addition, the AC to DC converter, the inverter, and corresponding control circuits must be duplicated within the conventional power supply within the computer or other electrical device. The customer must therefore in effect purchase two power supplies; a standard device power supply plus an uninterruptible power supply.